It would be really nice if there were a way to simulate using an AdBlocker extension.

Why? The biggest reason is that we often we have performance problems with ads, it's be nice to run a side-by-side with ads enabled vs. blocked to show the difference. The other is that ad performance can vary from page load to page load as different creative units are served, this variability is obviously bad for determining a baseline.

In most cases there are a lot of ad domains that would need to be blacklisted and they'll vary per page load since many are served by competitive ad marketplaces (Double Click for Publishers, Adnexus, etc...).

Any ad blocker with a reasonably up to date list would work. It could be an additional browser choice just like one would choose Chrome, IE10, IE11, etc... there could be a single option for "Chrome w/ Adblock Plus"

(08-22-2016 09:23 PM)jb510 Wrote: In most cases there are a lot of ad domains that would need to be blacklisted and they'll vary per page load since many are served by competitive ad marketplaces (Double Click for Publishers, Adnexus, etc...).

Any ad blocker with a reasonably up to date list would work. It could be an additional browser choice just like one would choose Chrome, IE10, IE11, etc... there could be a single option for "Chrome w/ Adblock Plus"

The fact is that there is those days dozens of domains due to RTB, but if you block the RTB themselves (doubleclick and co.), dozens of domain are not contacted anymore.
In the most bloated pages I've audited, blocking 20 domains was enough.
I still agree a simple "adblock" checkbox would be simple for us WPT users, I'm just saying it's not that easy to implement and that you have a not-that-painful alternative right now

Keep in mind that ad blockers also introduce some latency due to the required processing and parsing of HTML. This may be hard to trace in WebPageTest results, but you can see it in Chrome's Developer Tools.